In an image forming apparatus of an electrophotographic system, there is known a method of removing a transfer remaining toner adhering to a photosensitive body by a cleaning blade. With a configuration using the cleaning blade, a cleaning failure may occur when an image with a low coverage rate is continuously output, when an image is continuously output on sheets with a relatively small size (for example, postcard size), or when an image is continuously output under a high-temperature and high-humidity environment. To be specific, since the amount of toner to be supplied to the cleaning blade is decreased, the cleaning blade may be curled up or chatter (stick-slip) may occur. Hence, there is known a method of restricting a cleaning failure by intentionally supplying a toner to the cleaning blade.
Also, in an image forming apparatus including a plurality of image forming units each having a photosensitive body and a cleaning blade, there is known an apparatus that can select one of modes and executes the selected mode, the modes including a mode for image formation by using all image forming units (for example, full-color mode) and a mode for image formation by using a selected image forming unit (for example, monochrome mode).
When the mode for image formation by using the selected image forming unit (for example, monochrome mode) is executed, it is desirable to bring the photosensitive body of the image forming unit not used for the image formation into contact with an intermediate transfer body, so that part of the photosensitive body not used for the image formation does not slide on the intermediate transfer body.
However, if the photosensitive body is rotated without image formation, the amount of toner to be supplied to the cleaning blade is decreased, and a cleaning failure could possibly occur.
PTL 1 discloses an image forming apparatus including a plurality of image forming units each having a photosensitive body and a cleaning blade. In particular, to address a cleaning failure in an image forming unit not used for image formation when a mode for image formation by using a selected image forming unit is executed, there is disclosed a configuration that intentionally supplies a toner to the cleaning blade of the image forming unit not used for the image formation during non-image formation in the mode.
In this case, when image formation is executed by using the selected image forming unit, the photosensitive body in the image forming unit not used for the image formation is usually rotated without charging, exposure, or development. When a toner is supplied to the cleaning blade, a charge bias and a development bias have to be raised.
In this case, in a configuration that develops an electrostatic image by using a developer containing a carrier and a toner, since a timing is controlled to restrict adhesion of the carrier to the photosensitive body, it takes a relatively long time to raise the charge bias and the development bias. The toner is no longer supplied to the cleaning blade within a period corresponding to a sheet interval that is an interval between a current recording material and a next recording material in case of continuous image formation. Hence, productivity may be decreased. Owing to this, there may be conceived a method of applying only the development bias without charging the photosensitive body (setting the charge bias at OFF and hence causing the photosensitive body to be 0 V), and supplying the toner to the cleaning blade in the sheet interval.